The tooth size of the extinct early Pliocene megalodon shark teeth compared to the teeth of modern great white sharks. Image credit: Max Planck Institute for Evolutionary Anthropology
Megalodons are one of the largest carnivores ever lived on Earth, living in the global oceans of 23 to 3.6 million years ago, possibly up to 20 meters in length. Its extinction has been controversial.
Now, scientists have found that competing with great white sharks for food resources may have contributed to the extinction of megalodons. Although in comparison, the largest great white shark today is only 6 meters in total length. The results were published in Nature Communications on May 31.
The trophic level of an animal marks their place in the ecosystem, and diet plays an important role in understanding the lifestyle and ecological characteristics of a certain animal. Zinc is mixed in during tooth enamel formation and can be used as an alternative indicator to understand an animal’s diet and infer its trophic level in the ecosystem.
The researchers analyzed the stable isotope ratios of zinc in the teeth of modern and fossil sharks from around the globe, including the teeth of fossil megalodon sharks and modern great white sharks. The new method could allow scientists to investigate the nutritional levels of animals and understand where the animal’s feed is in the food chain. “We are the first to demonstrate that diet-related zinc isotopic features are preserved in the highly mineralized enamel crown of shark tooth fossils.” Thomas Tutken, a professor at the Institute of Earth Sciences at Johannes Gutenberg University in Germany, said.
Comparison of zinc isotope signals from fossils with modern sharks
Using the new method, the team compared the tooth zinc isotope features of multiple species that were extinct in the early Miocene (20.4 million to 16 million years ago) and early Pliocene (5.3 million to 3.6 million years ago) with the zinc isotopic features of teeth in modern sharks. They built a database of zinc isotopes for shark teeth, covering 20 extant shark species (including aquariums and wild individuals) and 13 fossil species including megalodon sharks.
They found that zinc isotopes were retained in shark teeth regardless of geological age, and that this zinc isotope value showed the nutrient level of the species. “We note the consistency of zinc isotope signals between fossils and modern similar taxa, which increases our confidence in the method, suggesting that zinc isotope values may have minimal differences based on marine food webs, which is a confounding factor in nitrogen isotope studies.” Co-author Sora Kim, a professor at the University of California, Merced, explains.
Subsequently, the researchers analyzed the proportion of zinc isotopes in the teeth of the early Pliocene megalodon, the proportion of zinc isotopes in the teeth of the early Miocene megalodon, and contemporaneous and modern great white sharks to investigate the effects of these iconic species on past ecosystems and between each other.
“Our findings suggest that both megalodons and ancestors were indeed top predators, higher in their respective food chains.” Michael Griffiths, a professor at William Patterson University, said, “But what is really remarkable is that zinc isotopes from the teeth of early Pliocene sharks in North Carolina suggest that the nutrient levels of early great white sharks overlap to a large extent with larger megalodons.” ”
Zinc stable isotope analysis of tooth enamel (the highly mineralized part of the tooth) was compared to more mature nitrogen isotope analysis of dental collagen (organic tissue in dentin), which is used to assess the extent of animal substance consumption. “On the timescale of our study, collagen was not preserved, so traditional nitrogen isotope analysis could not be performed.” Jeremy McCormack, lead author of the study and a researcher at the Max Planck Institute for Evolutionary Anthropology and Goethe Frankfurt University, explains.
Megalodons compete with the diet of great white sharks
The authors compared the zinc isotope values of megalodons and great white sharks and found that when they coexisted in the early Pliocene, their trophic levels overlapped and they might need to compete for the same food resources, such as marine mammals such as cetaceans.
“These results could mean that the prey of the two sharks overlaps at least somewhat.” Kenshu Shimada, a professor at DePaul University chicago, said, “While further research is needed, our results appear to support the possibility of megalodons competing in diets with early Pliocene great white sharks.” ”
New isotopic methods, such as zinc, provide a unique window into the past. “Our study illustrates the feasibility of using zinc isotopes to investigate the dietary and nutritional ecology of extinct animals over millions of years, and this approach can also be applied to other animal fossil populations, including our own ancestors.” McCormack concluded. (Source: China Science Daily Feng Lifei)
Related paper information:https://doi.org/10.1038/s41467-022-30528-9